Magnetic read heads are used in hard disk drives to sense magnetic signals from disks spinning beneath the read heads and, thus, to read data on the disks. To control the stability and magnetic moment orientation of the sensor layer of the head, a bias field is provided by hard bias magnet layers that are disposed next to the sensor layer at its two side edges.
As understood herein, a so-called “ultra contiguous junction” (UCJ) arrangement may be used to achieve a collinear relationship between the center of the hard bias layers and the center of the free sensor layer and thus avoid geometries that can lead to magnetic instabilities. Eliminating these instabilities can facilitate the read head reading higher density data recording, thus permitting a disk drive to store more data than it would otherwise be able to store.
The collinear relationship mentioned above is achieved by disposing a seed layer below the hard bias magnet layer to raise the hard bias magnet layer to the desired height vis-a-vis the nearby free sensor layer. However, as recognized herein, the presence of the seed layer can undesirably increase the electrical resistivity of the hard bias magnet stack. To counter this, the seed layer can be grown on a conducting layer such as gold (Au), but this in turn can undesirably reduce the magnetic coercivity of the stack, thereby frustrating the purpose of the hard bias stack in the first place. The decrease in coercivity is believed to be attributable to the loss of crystallographic orientation in the hard bias layer, which in turn is due to the lack of a desired crystal orientation developing in the seed layer when it is grown on gold or other body centered cubic (bcc) metals. Having recognized these considerations, the invention disclosed herein is provided.